1) Field of the Invention
This invention relates in general to a metal diaphragm valve which is widely used in the fluid pipings for semiconductor manufacturing equipment, and in more particular to such a device with safety means which can lock the valve in closed position.
2) Description of the Prior Art
A number of metal diaphragm valves with lock mechanism is widely used, which are capable of holding the valve in closed position. Of those conventional valves is mostly known the type which has a largely diamond-shaped knob to regulate the diaphragm for improved performance. It is so designed that the rotation of the knob is converted to a vertical reciprocation in a plunger that moves the diaphragm into contact with or away from a valve seat, thereby regulate the flow of fluid through the diaphragm.
With respect to FIGS. 4 and 5, which illustrate such a valve 23, a knob 21 is made rotatable on a horizontal plane between a first position where the valve is fully opened and a second position where the valve is fully opened. The first and second positions may be spaced by a rotational angle of 90 degrees. The flow of fluid through the diaphragm is precisely regulated by turning the knob 21 for a specific angle of degree between the first and second positions. The conventional locking mechanisms for these valves normally comprise a pair of stoppers 18 and a stopper pin 19 movable between the stoppers.
It is noted, however, that the prior-art lock mechanisms have difficulties in that the knob 21, when not fully turned to the closed position, tends to accidentally rotate by a casual touch of a hand or an object that happens to come near it. The diaphragm unwontedly lifts off from the valve seat to allow flow of the fluid, resulting in an serious accident.